Currently, terrestrial tuners are built as hybrid devices using limited number of small ICs, metal shield can and external discrete components such as manually tuned coils and varactors. Significant progress has been made in integration of cable tuners. Most of these devices are integrated on one chip with two external ceramic or surface-acoustic wave (SAW) filters and a few several other discrete components.
A reason for the slow progress in integration of a terrestrial TV tuner is the extremely demanding environment of off-the-air reception. The main problem is high power, out of band interferers such as cellular phone services that are close enough to the TV band. Another source of interference is high power in-band TV signals from other TV broadcast stations that the tuner is not presently tuned to. This problem is often referred to as near-far station problem. The two remaining design challenges are the required high image rejection ratio, IRR>65 dB and the required overall low noise figure, NF<8 dB of the tuner for different gain settings.
All these requirements can be met separately. However, their simultaneous meeting poses a substantial challenge for a fully integrated receiver. The existing dual-conversion cable-tuner architectures are not suitable for the implementation of a fully integrated terrestrial tuner for three reasons. They do not include any pre-filtering at RF, and therefore for the terrestrial application the low-noise amplifier (LNA) and mixer are overloaded such that their linearity requirements are difficult to meet. Next, double conversion systems are prone to excessive power consumption while attempting to meet the stringent intermodulation specs such as CTB, CSO and X-MOD. Furthermore, near-far station problem causes the severe noise and distortion degradation. Finally, their image rejection, typically in the 50-60 dB range, is not sufficient for terrestrial application.